It is well known that space time transmit diversity (STTD) can achieve symbol level diversity which significantly improves link performance. STTD code is said to be ‘perfect’, therefore, in the sense that it achieves full space time coding rate (Space time coding rate=1, also called rate-1), and it is orthogonal. When the number of transmit antennas is more than 2, however, rate-1 orthogonal codes do not exist.
Multiple Input Multiple Output (MIMO) technologies have been proposed for next generation wireless cellular systems, such as the third generation partnership project (3GPP) standards. MIMO systems use multiple antennas for both transmission and reception. Because multiple antennas are deployed in both transmitters and receivers, higher capacity or transmission rates can be achieved.
When using the MIMO systems to transmit packets, if a received packet has an error, the receiver may require re-transmission of the same packet. Systems are known that provide for packet symbols to be mapped differently than the original transmission.
In a closed loop system, the packet receiver can also indicate to the transmitter the best mapping of the re-transmit format.
In known systems, the possibility exists for certain symbol mappings to be ineffective in overcoming interference.
Thus a need exists for an improved ways to facilitate MIMO re-transmissions.